Acadia National Park in Bar Harbor, Maine is one of my favorite places to ride. Spectacular scenery along the coast with one way traffic flow and a climb up Cadillac Mountain to top it off if you wish a challenge. .
And it also has miles and miles of carriage trails for those who prefer that type of surface with no vehicles only the occasional horse drawn carriage.
I have biked across the US (using Adventure Cycling Maps ofc) and Acadia still remains one of my favorite places to bike.
It is always best to include popovers at The Jordan Pond House.